The question of political sovereignty must at all times be of acute academic interest, since it is practically impossible to say anything about the state without implying something about sovereignty, or vice versa. Political theory has very generally found this conception central to its inquiry; but in recent years the notion has been thrown into sharp relief by political events. In Fascism and Nazism the doctrine of state sovereignty is “made flesh” in startlingly substantial forms. These modern incarnations of Leviathan, and their threat to much which has come to be deeply valued, give unprecedented importance to an age-long discussion. Political theory is not to-day, if it has ever seemed, a simply academic issue, or an “arm-chair” branch of philosophy. Not all of those who carry through revolutions, who build barricades and defend them with their lives, have a clear philosophical theory of the state; but powerful beliefs and motives they certainly have; and it daily becomes more manifest that unless the world is content to allow its political future to be determined more and more by obscure visceral impulses or crude economic motives a more intense effort to achieve and to apply true beliefs in the political field is imperative.